From the Guidelines
The most appropriate next step in management for this patient is targeted ultrasound examination. When a pregnant woman at 15 weeks' gestation presents with an elevated maternal serum alpha-fetoprotein (MSAFP) level but normal estriol and β-HCG levels, a targeted ultrasound examination is the initial diagnostic test of choice, as it allows for direct visualization of the fetus to assess for structural abnormalities, such as neural tube defects, and confirm gestational age 1. Elevated MSAFP can indicate several conditions, including neural tube defects, ventral wall defects, multiple gestation, or incorrect gestational dating.
Key Considerations
- The optimal time for neural tube defect (NTD) screening is at 16 to 18 weeks gestation, but testing can be done between 15 and 20.9 weeks, and the laboratory should be informed of the gestational age at the time the sample was drawn for an accurate interpretation 1.
- Ultrasound dating of the pregnancy reduces the false-positive rate and increases the detection rate of NTDs.
- The test is most accurate if the laboratory is also informed of maternal weight, race, presence of insulin-dependent diabetes, number of fetuses, and family history of NTD, which are used to adjust the multiples of the median (MoM) level 1.
Next Steps
- If the ultrasound reveals abnormalities, then more invasive testing like amniocentesis might be considered as a second step.
- Genetic counseling is recommended for pregnancies with an elevated MSAFP test result, regardless of the ultrasound findings 1.
Rationale
Starting with a targeted ultrasound examination is appropriate because it carries no risk to the pregnancy while providing valuable diagnostic information that may explain the elevated MSAFP finding. This approach prioritizes the patient's safety and well-being while guiding further management decisions based on the most current and accurate information available 1.
From the Research
Next Steps for Pregnant Women with Elevated MSAFP Levels
- For a pregnant woman at 15 weeks' gestation with elevated MSAFP levels and normal serum estriol and β-HCG levels, the next step would be to undergo ultrasonography to confirm the presence of any fetal anomalies 2.
- Ultrasonography has been shown to be 100% sensitive and 100% specific in diagnosing neural tube defects in pregnancies with elevated AF-AFP concentrations 3.
- The predictive value of a positive ultrasound diagnosis is 100% and of a negative ultrasound 99.9% for neural tube defects 2.
- In addition to neural tube defects, ultrasonography can also detect other structural abnormalities, such as abdominal wall defects, chromosomal abnormalities, and urinary tract abnormalities 2.
- The use of ultrasonography can help avoid the risks of amniocentesis and provide a reliable diagnosis of fetal anomalies 2.
- It is also important to consider the clinical interpretation of maternal serum alpha-fetoprotein concentrations, taking into account factors such as maternal weight, race, residence, and gestational age 4.